Research On The Local Atomic Structure Of Amorphous Alloys Using The Ab-initio Molecular Dynamics Simulation

Amorphous, whose atomic arrangement does not have the transitional periodicand long-rang order, refers to a special kind of material, which only shows theshort-range and medium-range order. Since1960, a variety of atomic models of bulkamorphous alloys have been proposed on the basis of all kinds of research methods.Such as Hard-sphere random close-paced model, the microcrystal model, continuousrandom gird model, FCC close-packed clusters packing model. These atomic modelshave their own merits especially in explaining the unique physical and chemicalproperty of amorphous alloy. For further understanding atomic packing in amorphousalloys, especially the unique glass transition phenomena, Fan and his collaboratorsproposed the tight-bond cluster model and advanced the interconnecting zone as thecore concept of this atomic model. The tight-bond cluster model is the key point of thispaper.Based on the tight-bond cluster model, the local atomic structure of Zr55Cu35Al10bulk amorphous alloy is researched systematically. We employed neutron scatteringtechnology on Zr55Cu35Al10bulk amorphous alloy samples and completely crystalizedsamples in order to collect the data of structure function and then get the pairdistribution function. By constructing reasonable initial structure and employing theab-initio molecular dynamics methods we obtained three-dimension atomic structure ofZr55Cu35Al10amorphous alloys. A new simulation method of combining the ReveresMonte Carlo method and the ab-initio molecular dynamics method was proposed inthis paper, the atomic structure obtained by this new simulation method is reasonablealso, and is more representative because it once fitted the experiment data by theReveres Monte Carlo simulation.In this paper, we overlapped the experimental pair distribution function curve ofthe as-cast Zr55Cu35Al10and its completely crystallized counterpart, and combinedwith Lindemann’s Melting Criterion we concluded that the interconnecting atomicpairs can be reasonably defined as those pairs with their bonding lengths in the rangeof5%greater and10%smaller than their atomic radius, and the free volume is theatom pair distance10%greater than their atomic radius, and the distance of the clusteratomic pairs is5%smaller than their atomic radius.According to the range of pair distance of three zones in the tight-bonds cluster model, the atomic structure of the tight-bonds cluster was studied systematically andwas defined as atomic structure with center atom’s CN greater than12and tightbonded with other atoms. And we also defined the radius of cluster as the averagedistance between center atom with other atoms, and the radius represents the size ofcluster. Then we find that the sizes of different tight-bond clusters with the same centeratom are similar, but there are characteristic dimensions for different tight-bondclusters with different center atoms.